Spark plug or the like



H. A. BRINSON SPARK PLUG OR THE LIKE May 23, 1950 Filed 001;. 21, 1944IN VEN TOR. HG/"f'y A. BP/nson ATTORNEY Patented May 23, 1950 SPARK PLUGOR THE LIKE Harry A. Brinson, Sidney, N. Y., assignor to Bendix AviationCorporation, New York, N. Y., a

corporation of Delaware Application October 21, 1944, Serial No. 559,684

4 Claims.

This invention relates to sealing means and more particularly to meansfor sealing the bore of an insulator in a spark plug of the type usedfor igniting the combustible charges in the cylinders of internalcombustion engines and the like.

One of the objects of the present invention is to provide a novel sparkplug structure which is so constructed that leakage of gases between thecenter electrode and the insulation therefore is wholly or substantiallyeliminated at substantially all operating temperatures.

Another object of the invention is to provide novel sealing meansadapted for use in the bore of an insulator or the like, particularlyaround a core such as an electrical conductor.

A further object is to provide novel means for sealing the bore of aninsulator in the center electrode assembly of a spark plug which willalso function as means for securing an electrode or a terminal or bothin said bore.

Still another object is to provide novel sealing means for the bore ofspark plug insulating means or the like which may be readily andefficiently installed therein and which will withstand high operatingtemperatures and wide or sudden changes in temperature.

The above and further objects and novel features of the invention willmore fully appear from the following detailed description when the sameis read in connection with the accompanying drawings. It is to beexpressly understood, however, that the drawings are for the purpose ofiilustration only and are not intended to define the limits of theinvention, reference for this latter purpos being had primarily to theappended claims.

In the drawings, wherein like reference characters refer to like partsthroughout the several views,

Fig. 1 is a half sectional elevation view of one form of radio shieldedspark plug embodying the present invention; and

Fig. 2 is a bottom end view of said spark plug.

The single embodiment of the invention illustrated in th drawings, byway of example, is shown in the form of a radio shielded spark plug ofthe general type universally used in presentday aircraft engines, but itwill be understood that the features of the invention are equallyapplicable to other types of shielded spark plugs as well as to sparkplugs which are not of the shielded type. In the form shown, the sparkplug comprises a tubular metallic shell which is ex- ,ernally threadedat H for cooperation with a threaded opening in an engine cylinder (notshown) in a manner well understood in the art. The bore through shell I0is provided with a tapered wall portion l2 for a purpose which will morefully appear hereafter. A ground electrode 13 having bendable prongs 2|or of any other suitable known construction is secured in the lower endof shell ID by means of silver solder or other suitable means.

Ground electrode I3 is in cooperative spark gap relation with theenlarged head portion [4 of a center electrode l5 which constitutes apart of the conducting means mounted in the differential bore l6, ll ofa ceramic or like insulator l8 for conducting high tension electricalcurrent therethrough. In the illustrated embodiment, the head H of thecenter electrode engages the lower end of insulator l8 and the elongatedspindle l9 thereof extends through the small or reduced portion l6 ofbore I6, I! and terminates in the larger portion II thereof. The upperend of spindle I9 is provided with one or more annular grooves 20, orother suitable deformations, for a purpose to appear hereafter.

Means are preferably provided for mounting center electrode IS in thebore of insulator l8 in a manner whereby accurate centering of theelectrode in the insulator bore Hi and good heat conduction from theelectrode to the insulator are insured without subjecting the insulatorto the danger of being cracked by expansion of the electrode. As shown,spindle IQ of the center electrode has the diameter thereof slightlyreduced for a major portion of its length in bore 16 to form shoulders22, 22. The diameter of the parts of spindle l9 adjacent the ends ofsaid reduced portion, 1. e., the diameter of said shoulders, is slightlyless than the diameter of bore it, the exact clearance of these parts inthe bore being determined by the accuracy with which the insulator I8 isconstructed. The surface of the central reduced portion of spindle I9 ispreferably roughened somewhat, such as by sand blasting, and severallayers 23 of thin metallic foil, or the like, such as nickel or silverfoil, are wrapped around the same, the number of layers or turns beingjust suflicient to provide a relatively tight sliding fit in bore IS.

A metallic terminal 24 adapted for suitable connection with an incomingsupply cable carrying high voltage electrical current is installed inthe upper end of the bore I! in insulator 18. The adjacent ends ofterminal 24 and spindle l9 are spaced from one another and areelectrically connected by means of a resistor 25 and a wire 26 2,sos,as4

of relatively small radial cross-section. Resistor 25 may be eliminatedand replaced by other suitable conducting means or by an extension wire26. If the resistor is used for the purpose of reducing erosion of theactive parts l4 and 2! of the electrodes I 3 and iii, the same may havea resistance value of anywhere between approximately 75 ohms-to 10,000ohms. The preferred value of resistor 25 is approximately between 500ohm and 1,000 ohms. Conductor 26 may be made of any suitable type ofwire, such as Nichrome or molybdenum, and preferably has a diameter ofonly a few thousandths of an inch. One end of said conductor is securedto the upper end of spindle l9 before the latter is inserted ininsulator II and the free end thereof is preferably coiled to form aspring adapted to yieldably and electrically engage resistor 25 orterminal 24.

Novel means are provided in bore ll of insulator I! for sealing saidbore against leakage of gases therethrough from the engine cylinder andfor securing electrode I and terminal 24 in the insulator. The novelsealing material 21 is preferably, though not necessarily, electricallynon-conductive and completely fills the annular space around theconducting elements I9, 24, 25 and 26. The sealing material has a highmelting point and in its final form is a unitary rigid mass which hasinterlocking relation with spindle 19 at grooves 20 and with terminal 24at groove 28 or other similar deformations. in said spindle and terminalto thereby hold the parts in assembled relation.

The novel sealing material 21 is formed by fusing a mixture of powderedbore-silicate glass or other similar material having a high meltingpoint, such as "Pyrex glass, and one or more other powdered substanceshaving lower melting points, such as lead oxide, for example. Onesuitable mixture which has been found to be practical and useful informing a seal in bore i1 consists of one part by weight of powderedboro-silicate glass, such as Corning Pyrex glass No. 774, and one partby weight of powdered lead oxide. These proportions are not critical,however. It has been found practical, for example, to employ mixturesconsisting of from 20 per cent to 60 per cent lead oxide and 80 per centto per cent glass, the proportions being in terms of weight. One of theconsiderations, insofar as spark plugs are concerned, is to provide asealing material which will be plastic-like or pasty only when heated toa temperature above the maximum operating temperature of the spark plugbut below any temperature which might be detrimental to the spark plugparts, i. e., to the insulator I 8 and the parts installed in the borethereof. This result may be obtained by using the above mixtures sincethe melting point of the glass component although not definite is above1832 F., and that of lead oxide is 1630 F. The glass component willgenerally begin to soften at approximately 1472" F., but a considerablyhigher temperature is required to melt it. The mixture of the powderedglass and lead oxide is in effect a eutectic mixture which will softenat approximately 1400 F., a temperature below the softening and meltingpoints of the constituents thereof. Accordingly, when the mixture isheated to temperatures between approximately 1500 F. to 1800" F., thesame is reduced to a pasty or plastic-like compound. Although themelting point of the glass component is higher than 1500 F., the glassparticles of the mixture soften somewhat at temperatures aboveapproximately 1400 F. in the presence of the lead oxide and a certainamount of chemical reaction is believed to take place and unite the leadoxide particles with the Pyrex glass particles. The resulting materialsolidifies to a unitary homogeneous mass on cooling, said mass being aform of lead boro-silicate glass.

In forming the seal for the center electrode assembly of a spark plug ithas been found suitable to make the boro-silicate glass component of themixture by firing 80.5 parts by weight of silicon dioxide with 12.3parts of sodium tetraborate, 7.8 parts of boric acid, 2.2 parts ofaluminum oxide and .6 part of potassium carbonate. When thisbore-silicate glass is mixed with equal parts of lead oxide and fused inthe manner hereinafter pointed out, the resulting product has a chemicalanalysis of 40.25 per cent silicon oxide, 6.45 per cent boric oxide, .2per cent potassium oxide, 1.9 per cent sodium oxide, 1.1 per centaluminum oxide and 49.9 per cent lead oxide.

When the foil wrapped center electrode with conductor 26 secured theretohas been inserted into insulator I8, a predetermined quantity of thesealing material 21 in finely divided powder form is placed in bore llof the insulator. The components of the sealing mixture should bethoroughly and intimately mixed and it is desirable that the same besufficiently fine to pass a mesh screen. In order to insure goodelectrical contact between resistor 25 or terminal 24 and conductor 26,the latter should extend to or slightly beyond the upper surface of thepowdered mixture at this stage of the assembly. After the powderedsealing material has been settled, such as by vibration of the assembly,tamping, or the like, the assembly is placed in a chuck on a press andresistor 25 is set on the surface of the powder in contact with thecoiled end of conductor 26. Terminal 24 may be magnetically or otherwisesuitably supported by the plunger of the press and lowered intoengagement with the resistor 25. While a longitudinal compressionpressure of approximately 50 pounds is being applied to the parts by thepress, one or more flames are applied to the outer surface of insulatorIt, or other suitable means are employed to raise the temperature of thepowdered mixture to the approximate temperatures heretofore mentionedfor melting the-lead oxide or other equivalent component of the mixtureand bringing about the chemical re action between the lead oxide and thePyrex glass. The mixture is thus rendered pasty or plastic whileresistor 25 and terminal 24 are forced into final position by thepressure applied by the press. When the parts reach the positionsillustrated in the drawings, the source of heat is removed and as soonas the parts have cooled somewhat at normal room temperature the centerelectrode assembly, completed except for minor machining operations, isremoved from the press for mounting in shell Hi.

The novel center electrode assembly when thus sealed against the leakageof gases is preferably mounted in shell ill in such a manner as toprevent any leakage of gases between insulator i8 and the shell. Thismounting may be efiected, for example, by wedging a sleeve 30 ofrelatively soft metal such as copper between the surface of insulator l8and tapered wall l2 in shell i0, said sleeve being held within the shellby a shielding barrel assembly consisting of a metallic barrel 3|surrounding a rigid sleeve 32. Barrel 3i may be silver soldered, as at35, or otherwise suitably secured in shell ID or the same way may beformed integrally with the shell. Annular shims 33 made or" mica,asbestos, Or the like, may be interposed between insulating sleeve 32and metallic sleeve 30 to insure proper longitudinal dimensions mam anovel sealing material which may be readily.

installed and which will be eflective at all temperatures to which thespark plug is subjected during engine operation. Also, the novelsealing.

means comprehended by the invention will withstand rough handling andmay be installed readily and inexpensively in mass production byrelatively unskilled workmen. Additionally, the novel sealing materialhas an amnity for and, hence, adheres well to the insulator l8, spindlel9, and terminal 24.

Although only a single embodiment of the invention is illustrated anddescribed, it is 'to be expressly understood that the same is notlimited thereto. For example, it will now be apparent to those skilledin the art that the invention may be practiced with other than ceramicinsulators. Accordingly, the term ceramic, as used in the foregoingspecification and the claims. is to be interpreted to include othersimilar insulators such as aluminum oxide or the like. will also beapparent to those skilled in the art that the invention is equally asapplicable to unshielded spark plugs and other types of shielded sparkplugs as it is to the specific type shown. The invention is alsoapplicable to structures other than spark plugs when it is desired toseal a passage in materials having melting points below the assemblytemperatures employed. The external contour of insulator Il may begreatly varied and the manner of mounting the same in the spark plugshell may be materially changed. It will also be apparent that materialsother than those specifically mentioned as being suitable for thevarious elements of the spark plug may be used without departing fromthe invention. Various changes may also be made in the design andarrangement of the parts illustrated without departing from the spiritand scope of the invention. For a definition of the limits of theinvention, reference is had primarily to the appended claims.

What is claimed is:

1. In the center electrode assembly oi a spark plug, an insulator havinga bore therein, an electrical conductor in said bore, and sealing meansfilling a portion of said bore around said conductor consisting of afused mixture of bore-silicate glass and lead oxide.

2. A center electrode assembly for a spark plug comprising an insulatorhaving a bore therein, an electrical conductor in said bore, saidconductor being smaller in transverse cross section than the part of thebore in which it is situated, and means sealing the space in said borearound said conductor and consisting essentially of glass and a fusedmetal oxide of the type useful in glass making having a melting pointlower than the melting point of the glass.

3. The method of sealing the bore of a ceramic spark plug insulator thatincludes the steps of inserting in the bore a powdered mixture ofborosilicate glass constituting about to 40% of the mixture, and of leadoxide constituting about 20 to 60% of the mixture, and heating themixture to a temperature at which the lead oxide is molten and the glassis softened.

4. A spark plug having a conductor sealed within a ceramic insulator bya composition analyzing 40.25% S102, 6.45% 320:, 0.2% K20, 1.9% NazO,1.1% A:, and 49.9% PbO.

HARRY A. BRINSON.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Number Name Date 1,508,455 Kraus Sept. 16, 19242,210,489 Lemmens Aug. 6, 1940 2,221,709 Hood Nov. 12, 1940 2,248,415Schwartzwalder July 8, 1941 2,293,381 Carington Aug. 18, 1942 2,304,562Gerisch Dec. 8, 1942 2,311,647 Doran Feb. 23, 1943 2,317,305Schwartzwalder Apr. 20, 1943 2,349,432 Hopps May 23, 1944 2,351,128Jeflery June 13, 1944 2,353,354 Nordberg July 11, 1944 2,355,163 JacksonAug. 8, 1944 2,408,642 Hopps et a1. Oct. 1, 1948

